sobel etal



Oct. 10, 1961 l. J. SOBEL ETAL 7 VIBRATORY PIEZOELECTRIC TRANSDUCERSFiled April 1, 1959 2 Sheets-Sheet 1 I.J.Sobel E.Lessing ATTOR NEYSUnited States Patent" 3,004,177 r VIBRATGRY .PIEZOELECTRIC TRANSDUCERSIlyitch J. Sobel, 16-26 163rd St., Whitestone 57, Long Island, N.Y., andEdward Lessing, 7 Keller Lane, Dobbs Ferry, N.Y.

Filed Apr. 1, 1959, Ser. No. 803,475 4 Claims. (Cl. 310-92) Thisinvention relates to vibratory piezoelectric transducers, such as thoseused in audio-frequency devices for transducing audio-frequencyvibrations into corresponding electric signals or vice versa, althoughthe invention is applicable to such transducers operating within anyother frequency ranges.

In many applications, piezoelectric vibratory transducers having theform of a longitudinal beam have to be clamped at two longitudinallyspacedbiasing or clamp ing regions thereof for causing them to vibratewith the desired response. Thus, for microphones designed for operationwith optimum sensitivity, it is desirable to fix the resonant frequencyof the piezoelectric transducerwell below the upper frequency limit ofthe frequency range of such microphones, such as about 1 to 1 /2 octavesbelow the highest frequency of its range. On the other hand, formicrophones which are to operate with a flat.

frequency response over a predetermined frequency range and where thesensitivity of the microphone may be sacrificed, the resonant frequencyof the transducer may be set nearer the upper limit of the desiredfrequency range. In the past, piezoelectric transducers of this typehave been clamped at two spaced regions by distinct sets of elasticclamping members, and the assembly of such complete piezoelectrictransducer devices required accurate location of the two clampingmembers at the accurately spaced longitudinal portions of thepiezoelectric transducer. As a result, mass production ofelectroacoustic transducer devices operating with such piezoelectrictransducers, presents difiiculties because of the non-uniformity in theoperating characteristics of the completed assembled devices due tovariations in the location of the two spaced clamping members along thevibratory piezoelectric transducer thereof.

An object of the invention is to simplify the manufacture ofelectromechanical transducer devices operating with such clampedpiezoelectric transducers and to assure a materially higher degree ofuniformity of their operating characteristics when manufactured on amassproduction basis.

The present invention is based on the discovery that piezoelectrictransducer devices wherein a piezoelectric transducer member operateswith a movable transducer region extending between two longitudinallyspaced clamp regions thereof, may be manufactured with a much higherorder of uniform operating characteristics than heretofore possible, byproviding the piezoelectric transducer body with an integral elastomerclamping body which extends along the entire length of the movabletransducer region thereof and has two spaced clamping wall sectionswhich are held clamped to two longitudinally spaced clamping regions ofthe transducer member for securing the desired operating responsethereof. 7

The foregoing and other objects of the invention will be best understoodfrom the following description of examplifications thereof, referencebeing had to the accompanvin g drawing wherein:

FIG. 1 is a vertical cross-sectional view of a microphone transducerdevice exemplifying one form of the invention; 7 a V FIG. 2 is across-sectional view along line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view of the central region of the transducerdevice along line 3--3 of FIG. 1;

FIG. 4 is a vertical cross-sectional view of the internal transducerassembly of the transducer device along line 4-4 of FIG. 2;

FIG. 5 is an end view of the transducer assembly of FIG. 4 from the leftend thereof;

FIG. 6is an end view of the transducer assemblyof FIG. 4 from the rightend thereof; and Y FIG. 7 is an exploded view of the elements of thetransducer assembly shown in FIGS. 46.

Although piezoelectric transducer devices of the invention may be usedin any of the various known audiofrequency and supersonic-frequencytransducer devices, and also in other applications, it will be describedin connection with a high fidelity microphone of the type generally usedin high fidelity audio-frequency systems operating with a uniformfrequency response over thefrev quency range up to about 13,000 c.p.s.

Referring to the drawings, FIGS. 1-3 show a microphone adapted to pickup acoustically transmitted sound signals and transduce them intocorresponding electric signals. However, the electro-acoustic transducerof such microphone will also transduce electric signals impressed on theelectrodes of its piezoelectric transducer into corresponding acousticoutput.

The microphone shown operates with a conventional piezoelectrictransducer 21 (FIGS. 4-7) having an elongated axis. The transducer 21may be formed of two strip-like ceramic piezoelectric transducerelements soldered to opposite sides of a central metal sheet elementfaces 22, with the underlying two ceramic body sections beingelectrically polarized in differential relation for generating aidingvoltages when the transducer 21 is subjected to bending or'strains in adirection transverse to its electrode surfaces, such as disclosed inKoren et al. Patent 2,863,076. The piezoelectric transducer 21 shown hasmetallic surface electrodes on its external electrode surfaces 22.

A microphone of the type herein described may be designedto operate withsubstantially uniform response over a wide range of audio frequencies,for instance, between 30 c.p.s. and 13,000 c.p.s. This in turn requiresthat the ceramic transducer 21 should resonate or have a resonantfrequency at about 4500 c.p.s. This necessitates that the two spacedclamping regions of the elongated transducer 21 be held clamped by twospaced clamping bodies so that the vibratory regions of thepiezoelectric transducer extending between and beyond the two clampedregions thereof shall vibrate with the desired high resonant frequency.

In accordance with the invention, piezoelectric mechano-electrictransducer devices are manufactured on a mass-production basis with ahigher order of uniform operating characteristics than heretoforepossible, by providing their vibratory piezoelectric transducer with anintegral clamping body of elastomer material having two sets of spacedintegral elastomer clamping sections which are held clamped againstlongitudinally spaced outer surface portions of two spaced clampingregions of the piezoelectric transducer for restraining movement of theclamped transducer regions while the intermediate and any othervibratory regions thereof remain free from clamping engagement and arefree to vibrate .with the desired high resonant frequency.

In the device shown, the" transducer 21 forms part of a transducer'as'ser'nbly generally designated 29, comprising an elastomer clampingbody 3% and a rigid mounting structure 4t) which serve to hold thetransducer 21 in'its operative vibratory position Within the rigidmountingstructure. The elastomer bodylsil may be made of elasticrubber-like organic solid material such as a vinylchloridecompou'rid,"or the like,"which embodies sufficient plasticizersubstance to serve as a solid elastic elastomer body, portions of whichmay be clamped against opposite surface portionsof the piezoelectrictransducer 21 for 'restraining'motion thereof without causing fractureof the relatively fragile piezoelectric body of such transducer. In theform shown,th'e' elastomer clamping body 3%) has a hollow interior space31 within which a substantial axial length of the transducer 21 is'free'to vibrate. The integral elastomer clamping body 39 has anintermediate junction body portion which is free from clampingengagement with the intermediate vibratory transducer region 25, and ateach of its two opposite ends two sets of two opposite elastomerclamping wall sections 32, 33 respectively, held in clamping engagementwith the two clamped transducer regions 24 embraced thereby forrestraining their vibration motion, while the intermediate vibratoryregion 25 of the transducer remains free to vibrate. Proper clearancespacing 'is' thus provided between the inwardly facing surfaces of theintermediate junction body portion of the elastomer clamping body 36 andthe facing surfaces 22, as well as the side edges of the freelyvibrating intermediate transducer region 25 extending along the majorlength of the hollow space 31 of the transducer-clamping elastomer body3-9. i

"The rigid mounting structure so may be made of any hard, rigidmaterial. In the form shown, the mounting structure 40 is of hardsynthetic resin material, as by molding, and has sutiicie'nt rigidity toresist deforma-V t'i'on and provide strong mounting forces whereby thetransducer 21 with its elastomer clamping body 30 are held in theiroperative positions relatively to the other elements of the'microphone.The rigid mounting structure this shown formedwith a'hollow interiormounting space 41 shaped to receive and hold fixed therein in properoperative position the elongated elastomer clamp ing body 39 with itstransducer 21. At one end of its hollow interior space 41 the mountingstructure 41 has one set of opposite rigid clamping walls 42 which arespaced fromeach other'by a clamping space of sufii c'iently small heightfor holding the embraced elastomer clamping wall sections 32 compressedand clamped against one embraced, clamped transducer region 2'4 forrestraining vibratory motion thereof. At the opposite end of its hollowinterior space 41, the integral mount ing structure 40 has a further setof opposite rigid clamping walls 42 which arespaced from 'each' other bya clamping space which is of sufficiently small height for holding theembraced elastomer clamping wall sections 32 compressed and clampedagainst the other embraced, clamped transducer region 24 for restrainingvibratory motion thereof.

In accordance with the invention, the height of the clamping spacebetween the set of rigid clamping walls 42 is greater than the height ofthe clamping space between the other set of clamping wall sections 43."In addition, the entire length of the hollow mounting space 41 of themounting structure extending to the right of clamping wall sections 43(as seen in FIG. 4), is made sufiieiently "wider than the thickness ofthe elastomer body extending to the left of its elastomer clamping wallsections 32, for permitting free entry and insertion of the narrower endof elastomer clamping body'30 into' the clamping space 41 until thenarrower left end of the elastomer clamping wall section 33 reachesthe'clamp ing space between the rigid clamping wall sections 43 ofmounting structure 40. This arrangement enables free and ready insertionof the narrower end of elaso- Wain d mer body 30 with the transducer 21and its terminal members 51, 51, held assembled tliiereon, into thehollow mounting structure 4% through the wider spacing between its rigidclamping wall sections 42, and free inward movement of the elastomerbody assembly toward the narrower spacing of the other set of rigidclamping wallsections 43' of" the rigid mounting structure 4%).Thereupon, the closer-spaced forward elastomer'clamp ing wall sections33 are forced into their" operative clamped position between thecloser-spaced rigid clamping wall sections 43 of the mounting structure4t), while the other set of the wider-spaced elastomer clamping wallsections 33' are forced intenam in engagement under the wider-spacedrigid clamping wall sections .42 of the rigid mounting "member41),"therebji completing the operative assembly of transducer 2i andelastomer clamping body 30' in precisely accurate clamping positionsthereof within the rigid mounting 'st'ructuredt 'In accordance with theinventioii,"the self-supporting transducer assembly of the typedescribed above, is combined with two strip-like metallic terminalmembers arranged to be held clamped to the electrodes of thepiezoelectric transducer, and having exposed external terminal portionsthrough whichexternal circuits are connected to electrodes of thetransducer structure 21. In the form shown, the transducer assembly 20'has two ter.- minal members 51, SS'made, for instance, of electricallyconductive sheet material which is also elastic, such as brass. Each ofthe terminal members 51, 55 has a mounting arm 52 and 57, respectively,bounded by tapered edges to fit between the tapered inward surfaces ofthe mounting compartment 41 of'th'e rigid mounting structure 40; The twoterminal'mounting arms 52,57 are arranged to'be'retained iri'fixedposition between the sidewise facing exterior surfaces of the side walls35 of the'elastotner'clamping body 36 (FIGS. EH7), and the inwardlyfacing "surfaces of. the side walls of the integraL'rigid mounting's'tructurefeii. Each terminal arm 52, 57 has a laterally extending flatcontact tongue portion 5358, respectively, formed out of a portionof'therespectiveimounting arm 52,52, as by cutting and bending. The twoterminal contact ton tea 53, 5e are held clamped in their operative po'between the underlying outer electrode surface port ns 22 of theendr'egions of the piezoelectric transducer and the overlying'el'astomer clamping wall portions 33 which are held clamped thereto by theoverlying rigid clamping "wall portions '45 of the rigid clampingstructur'e ltl. i i h "The side walls 35 of the elastomer clamping body39 are provided with cut-outs 36' (FIGS. 5, 7) through which thelaterally bent contact portions 53, 53 of the two terminal members 51,55 pass into engagement with the underlying'electrode'surface portions22 of ti piezo electric transducer 21. "Each of the two terminal strips51, 55 also has a laterally projecting terminal prong arm 54, 59 exposedto engagement with a suitable socket terminal element of the cooperatingexternal electric circuit to which it is'to be detachably connected.

In the form shown, the rigid clamping wall sections 42, 43,which'underlie the lower wall of the integral elastomer clamping body3%, form part of a rigid base wall 44 held seated agaihst'a 'wall ofcasing 60 and provided with a thicker base wall section 45 shaped to litand to be fixed within an opening'ol of the casing 69, in which thetransducer assembly 26 isoperatively mounted' In the form shown, thethicker base wall section 45 is of'cir'cular' shape, aiiditha's apolarizing ridge 45-]. arranged to fit in an oriented position in'thecorre spondingly shaped casing opening 61. The circular casing openingolhasa polarizing recess into which the polarii With this arrangement thetransducer assembly 20 is readily mounted in its operative positionalong the wall of itscasing 60 by dropping its base wall projection 45with its polarizing aligning ridge 45-1 into the seating opening 61 ofits casing 60, with the aligning recess of the casing opening engagingthe aligning ridge 45-1 of the base wall projection 45. The transducerassembly is secured into its operative position along the casing opensing 61, in which it is shown in FIGS. 1-3, by applying a coating of aknown good cement to the base wall, its wall projection 45, and theseating surfaces of the walls of the casing 60 and its opening 61engaged thereby before placing the mounting structure 40 of thetransducer assembly 20 in its operative position within the casing 60;

A feature of the invention involves an arrangement which makes possiblethe automatically aligned positioning of the elements of a transducerassembly of the type described above, for assuring that the elastomerclamping body is automatically fixed in its accurately aligned positionwithin the mounting structure 40 in the manner described above,notwithstanding the fact thatthe two metallic terminal members haveexternal terminal projections extending in a direction transverse to thedirection of the movement of the elongated elastomer body 30 into itscoaxial mounting space 41. To this end, the base wall 44 of thetransducer mounting structure 40 is provided on the side of itsgreater-spacing clamping wall sections 42 (FIGS. 3-7) with two elongatedslots 47 extending from the wall edge thereof toward its interior regionthrough which the outwardly projecting terminal arms or terminal prongs54, 59 project in laterally outward direction. This makes it possible tomove the elongated elastomer body 30 with the transducer 21 heldassembled therein, in the way shown in detail in FIGS. 47, with thecontact tongues 53, 58 of the two terminal members 51, 55 held in theassembled position along and partially within the elastomer body, intothe interior mounting space 41 of the mounting structure 40, in the waydescribed above, while the two terminal prongs 54, 59 which projectlaterally beyond the elongated elastomer body 30 move along the slots 47of the mounting structure base wall 44 into their final inward positionwithin the base wall slots 47 in which they are shown in FIGS 1, 3 and4-6.

With such arrangement, the inward boundary edge surface 48 of theprong-receiving slots 47 of the mounting base wall 44 serve as automaticstops which automatically stop the inward movement of the assembly ofthe transducer 21, the elastomer body 30, and the two terminal members51, 55, when they reach the inward operative position between the twosets of clamping wall sections of the mounting structure 40 by theautomatic assembling and aligning operating described above. I

In the transducer device the abutment between the terminal prongs 54, 59of the transducer assembly of elastomer body 30 and the stop edgesurface 48 in the terminal slots 47 of rigid mounting structure 40 fixestheir final aligned assembly position.

With such arrangement for automatically stopping the inward movement ofthe sub-assembly of the transducer elements which are combined with theelastomer body when they reach their operative position within theinterior of the rigid mounting structure 49, the two interior wallsurfaces of the mounting structure overlying the facing surfaces of theelastomer body 30 extending over the wide transducer electrode surfaces,may be given an inwardly tapering shape as indicated in FIG. 7.

However, if the transducer assembly of the type described above isprovided with externally exposed terminal portions (corresponding toterminal prongs 54, 59 described above), which extend in the same axialdirection as the piezoelectric transducer 21, such sub-assembly of theelastomer body 30 is providedwith a different type of stop elementscooperating with stops of the mounting structure 40 for automaticallystopping inward movement of the sub-assembly of elastomer body 30 whenit reaches the inward operative position. Byway of example, the inwardsurfaces of the mounting structure 40, near its rightward end, as seenin FIG. 4, may have inwardly extending stop shoulders or stops 49adjoining its two wider-spaced clamping wall portions 42, which mountingwall stops 49 are arranged to engage stop surfaces 39 formed on thefacing side surfaces of the outward regions of the two elastornerclamping wall regions 32. The stop surfaces 49 and 39 of the mountingstructure 40 and the elastomer body 30 are so arranged that when thesub-assembly of the elastomer body 30, of the type described above, ismoved inwardly into mounting space 41 of mounting structure 40,thesub-assembly of elastomer body 30 is automatically stopped at the endof its inward movement when'the elastomer clamping regions 32, 33 reachthe inward position in which they are forced into clamping engagementwith the clamped transducer regions 44 overlying clamping wall portions42, 43 of the mounting structure 40.

In the particular embodiment of the invention shown, the piezoelectrictransducer 21 is connected to a vibratory diaphragm 64 through amotion-transmitting member or link 65. Although the intermediatevibratory transducer region 25 extending between its two clamped regions24 may be coupled through such link to the diaphragm 64, the transducerdevice shown operates with a transducer 21 which has a further vibratorytransducer region 26 coaxial with the intermediate vibratory transdncerregion 25 thereof, and extending coaxially therewith beyond one of itsclamped regions 24, for instance to the right, as seen in FIG. 4. Thevibratory diaphragm is very light, and may be formed, for instance, ofthin aluminum foil. In the particular device shown, the diaphragm 64 isof circular shape, and its rim is secured, as by cement, to theunderlying edge of easing rim 63 of the circular casing 60. Themotion'transmitting link 65 has two inward grip arms 66 embracing withtheir notched end portions an end portion of the outer vibratory region26 of transducer 21, for'transmitting vibratory motionbetween it and thediaphragm 64. The outer end of the link 65 passes through the center ofthe conically shaped vibratory diaphragm 64, and is secured to theadjoining diaphragm portions in a conventional way, as by wax or cement.

To protect the delicate vibratory diaphragm 64 against disturbance fromthe exterior, it is covered by a protective cover wall 70, having slitopenings through which acoustic signals are transmitted between thesurrounding space and the diaphragm 64 for causing the diaphragm 64 tovibrate in accordance with the, sound propagated in the surroundingspace, or to cause the diaphragm to transmit acoustic energy or sound tothe surrounding space when vibrated by the vibratory transducer 21. Inthe form shown, the periphery of the protective cover wall is heldclamped against the underlying casing rim 6?. by an overlying inward rimprojection or flange 68 of a casing cover 69 secured to the exterior ofthe relatively rigid transducer casing 60. In the form shown, the casingcover 69 is formed of a relatively thick layer of elastomer orrubber-like material which is retained on the exterior of the casing 60by elastic forces and/or a layer of cement, and also by the overlappingengagement of the cover regions overlapping the upward and downwardsides of the microphone 6t as shown in FIG. 1.

The desired flatness of the response is achieved by damping means whichsuppress excessive acoustic motion in the region of theresonantfrequency of the transducer.

In accordance with the sole invention of the applicant Sobel, thedamping fabric and the separate hard and strong protective covergenerally used with high quality acoustic diaphragm transducers, isreplaced by a hard cover wall overlying and protecting the vibratorydiaphragm, the hard cover wall having one or more slits of minute widthand depth, which have negligible acoustic inertance while 7 7 providingthe desired'acousticdamping resistance which dissipates excessiveacoustic motion without appreciable sacrifice in over-all sensitivity.This s'ole invention constitutes the subject-matter claimed in theco-pending application Serial No. 825,083, filed July 6, 1959, by Li.Sobel, as sole inventor thereof. I

Without thereby in any way limiting the scope of the invention, buttoenable more ready fpractic'e thereof, there will now be given by wayof example, design data of embodiments of the invention:

I A microphone which has a substantially fiat open-circuit response overthe frequency range of 30 to about 13,000 c.p.s., has a diaphragm ofaluminum foil 1.2 inches in diameter. It has a piezoelectric ceramictransducer body .026" thick, .063" wide, and .425" long, formed of leadzirconate and lead titanate ceramic known as PZT. The clamped length ofthe ceramic transducer including its free vibratory portion is 300".'The clamping width (along its axis) between its metal terminal contact58 is .40". The clamping width at the opposite end .of the elastomerbody is .050. The thickness of the uncompressed elastomer body atitswider end is .160", and at its opposite narrower end, .130". Theoverhang of the outwardly projectingportion of the transducer to thepoint of its engagementwith the diaphragm drive rod is .100". The volumeof the casing'compartrnent underlying the diaphragm is large enoughtoassure that its acoustic stiffness has only negligible effect on themicrophone response. A conventional minute leak opening from thecompartment space provides pressure equalization on both sides of thediaphragm. The clamped piezoelectric transducer, without its linkconnection, resonates between 4000 and 4500 c.p.s. It operates with asensitivityof 63 decibelsbelow 1 voltfor-acoustic pressure of l dyne/cm.square.

A similar microphone which has a substantially fiat, open-circuitresponse between 13,000 and 16,000 c.p.s.,at a lower sensitivity of 68dbbelow 1 volt, for the same air pressure, has a shorter piezoelectricceramic transducer of .390" length,"and otherwise similar dimensions.

*A similar microphone which has a higher sensitivity of 5 8 db below 1volt for the same acoustic pressure and a substantially flat responseover the frequency range from 30 to 8000 c.p.s., has a longer ceramicpiezoelectric transducer of -.450"-length,'and the same otherdimensions. The clamped piezoelectric transducer without its drive linkconnection resonates between 2700 and 3000 c.p.s.

It will be apparent to those skilled in the art that the novelprinciples of the invention disclosed herein in com nection with thespecific exemplifications thereof will suggest various othermodifications and applications of the same. It is accordingly desiredthat in'construing the breadth of the appended claims, they shall not belimited to the specific exemplifications of the invention describedabove.

We claim:

1. In a mechano-electric transducer device, an elongated piezoelectrictransducer body with two opposite, relatively large, outer transducersurfaces and having an intermediate elongated vibratory transducerregion extending between two clamped transducer regions thereof, anintegr'al, hollow elongated elastomer body coextensive with andsurrounding the over-all length of said clamped and intermediatetransducer regions, said elastomer body having two spaced sets of twospaced, generally parallel restraining walls engaging with their innerelastomer sur faces the outer surfaces of said two clamped transducerregions, respectively, an integral, relatively rigid hollow mountingstructure coextensive with said elastomer body and having twocorresponding spaced sets of two spacedi opposite clamping wallsengaging and clamping with their" inner clamping surfaces the outersurfaces of said two sets of restraining walls for suppressing vibratorymotion of said two clamped transducer regions, said intermediatevibratory transducer region being relatively free for vibratorytransducer motion in a direction transverse to said transducer surfaces.

2. In a transducer device as claimed in claim 1, the height of oneclamping space between one of said two sets of clamping walls beinggreater than the height of the further clamping space between the otherset of clamping walls, the two sets of elastomer restraining walls beingof a height corresponding and complementary to the greater and smallerheights of said two clamping spaces of the mounting structure, wherebythe transducer assembly comprising said elongated elastomer body withsaid piezoelectric transducer body mounted therein may be freely movedwith its smaller-height restraining walls throughthe greater-heightclamping space of said mounting structure into its operative positionwithin said mounting strnc ture.

'3. In atransducer device as claimed in claim 2, an-

exposed electrode surface on eachof said two opposite transducersurfaces along at least one clamped transducer region, two L-shapedmetallic terminal strips extending with their strip surfacestransversely to said transducer surfaces, one mounting arm of eachterminal strip being held clamped by opposite side wall portions of oneset of said clamping walls to opposite side wall surfaces of thecorrespondingset ofelastomer restraining walls, and the other terminalarm of each terminal strip extending in the same general directiontransversely to said electrode surfaces, the mounting arm of each ofsaid terminal strips having a laterally extending contact portion heldin clamping contact engagement with a difierent one of the two oppoisteelectrode surfaces of the transducer body by overlying clamping walls ofsaid one set or" clamping walls.

4. In a transducer device as claimed in claim' 3, one clamping wall ofsaid mounting structure extending along said clamping space havingopenings through which the terminal strips project, respectively, beyondthe exterior of said two walls for contact engagement with externalcontact members, said one clamping wall having two slits extending fromsaid two openings, respectively, to the edge of said mounting wall,whereby said transducer assembly including said two terminal strips mayhe moved jointly into said operative position within said mountingstructure.

References Cited in the file of this patent UNITED STATES PATENTS

